The naysayers had already begun shoveling dirt on the Big Blue football grave of Eli Manning. The football obituaries were being written, the football eulogies were being sung.

So who was that in the red 10 jersey slinging the ball Tuesday at Giants OTAs?

Could that have been Eli Manning, starring in a “Night of the Living Dead” remake, produced by John Mara and Steve Tisch and directed by Dave Gettleman and Pat Shurmur? Who gave their franchise quarterback new life the night they drafted Saquon Barkley instead of Sam Darnold, Josh Allen or Josh Rosen?

E-life.

“I think Eli has a lot left in the tank,” wide receiver Sterling Shepard told The Post, “and they were right by making that decision, I feel like.”

Manning (19 TDs, 13 INTs in 2017) was granted his wish to keep his dream job, and now, at age 37, it is on him to author a dream season few on the outside believe he has in him.

Those on the inside feel differently.

Head coach Shurmur worked magic with Case Keenum in Minnesota last season and believes he can work magic with the eternally cerebral Manning.

A Barkley-centric running game behind a rebuilt offensive line will give Manning the kind of balance he has lacked for years, and a healthy Odell Beckham Jr. should make a dramatic difference.

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“Being at Duke (for spring workouts) with him, kinda seeing his routine, getting to see what he’s been doing, you can definitely tell he’s kinda turned back the clock a little bit,” tight end Evan Engram told The Post.

If you didn’t know how old he is, how old would you think he would be?

“I would say early 30s … like 30, 31,” Engram said.

“I expect a big year from 10. We got some dogs up front that are gonna work their butts off to protect him, we’re gonna work all together, have a good run game, and we got some weapons outside that’s gonna make a lot of plays for him, so I’m really excited to see what we could do.”

If you didn’t know how old Eli Manning is, how old is he looking these days?

“I’d say about 26, 27,” free safety Andrew Adams told The Post.

No way.

“Yeah, he looks about in his prime … throwing the ball well … got good zip on it … so yeah, he’s looking great,” Adams said. “He’s performing at a high level in these OTAs, definitely.

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Barkley will also serve as a safety valve in the passing game for Manning, who completed 105 passes to the backs last season. The difference is Barkley can take any one of them to the house.

“He’s a hard-nosed guy,” Adams said of Barkley. “He’s gonna put his head down and get you four yards no matter what.

“He can make nothing into a little bit, a little bit into a lot.”

If you didn’t know how old Manning is, how old would you think he was?

“The guy’s still out here slinging the ball like — I couldn’t give you a specific age, but he’s out here slinging the ball just like he always has,” Shepard said.

It all sounds good at the end of May. The jury is very much out. But Manning no longer has to look over his shoulder and worry about taking a seat on the bench. He loves being the quarterback of the Giants. It stings him that he has not won a playoff game since Super Bowl XLVI. He doesn’t merely want to win. He needs to win. Before his championship window is shut forever.